Centrifugal separator with oscillating scraper



E. F. SMALL CENTRIFUGAL SEPARTOR WITH 4OSCILLATINGr SCRAPER Filed April 25, 1945 3 Sheets-Sheet 1 Jan. 14, 1947.

E. lF. SMALL CENTRIFUGAL SEPARATOR WITH OSCILLATING -SCRAPER Filed April 25, 1945 3 sheets-sheet 2 Iriver! ar.

Ep WARD T 5MM# E. F. SMALL `CENTRIFUGAL SEPARATOR WITH OSCILLATING SCRAPER 3 Sheets-Sheet -3 Filed April 25, 1945 Patented Jan. 14, .1947

CENTRIFUGAL SEPARATOR WITH OSCILLATIN G SCRAPER Edward F. Small, Newton,

Machine Company,

Mass., assignor to Bird South Walpole, Mass., a

corporation of Massachusetts Application April 25, 1945, Serial No. 590,217

12 Claims.

This invention relates to centrifugal separation and particularly to a centrifugal machine useful for separating solids from liquid and for classifying solids of different characteristics in liquid suspension.

In the type of centrifugal operation which the invention principally concerns, the mixture of solids and liquids is carried upon the inner imperforate surface of a high speed rotary drum or bowl By centrifugal action, the solid component of the mixture, or the solid component of greater mass, concentrates at the bowl surface and is removed from the bowl by scraping along its surface. Apparatus for performing this operation has conventionally consisted of a generally cylindrical or conical centrifuge bowl having raised end edges over one of which the liquid overflows and over the other of which the solids concentrated at the bowl surface are scraped or swept by a screw conveyor, rotating within the bowl at a slightly different speed to provide the requisite relative rotation between the conveyor and the bowl.

Difiiculty has been experienced with apparatus of this sort in that the relative rotation between the conveyor and the bowl with its bed of concentrated solids causes extensive rubbing of the solids by the threads of the conveyor and also grinding of the solids between the conveyor threads and the bowl surface. In dewaterng or classifying many types of materials, the breakage of solids particles or Crystals resulting from this abrasive action is deleterious to the product and constitutes a serious Iimitation on the use of the machine. Moreover, at the high rotational speeds involved, under load conditions, the resistance to relative rotation developed between the bowl and conveyor, because of the very large amount of solid material in the operating load, is very great, causing large power and energy losses and necessitating the use of intricate speed reduction gearing in the drive to the two rotational bodies to maintain the speed differential between them.

The principal object of this invention is to provide novel apparatus by which centrifugal separation or classification is accomplished without these diiculties and with greater efficiency and at less power and machine cost than` has heretofore been possible. Preferred embodiments of the invention as hereinafter described, are illustrated in the accompanying drawings, where- 1n:

Fig. 1 is a, View largely in vertical longitudinal section, partially in side elevation, of a centrifuge according to the invention;

Fig. 2 is a front elevation View of the centrifugal bowl of the apparatus of Fig. 1 with the casing omitted and with the upper portion of the front of the bowl bro-ken away;

Fig. 3 is a view similar to Fig. 1 of a modified machine.

Referring to the accompanying drawings and flrst to the embodiment of Figs. 1 and 2, the may chine therein shown has a centrifugal drum Ill rotatable within a stationary housing I2 by means of a drive sleeve I4 fxedly connected to one end of the drum by means of a spider I6. Sleeve I4 is rotatably mounted in ball bearings I8 in a casing 20 which extends rearwardly from housing l2, and is operated by means of a. belt pulley 22 fast thereto.

The inner or bowl surface 24 of the drum is concave longitudinally of the drum axis, its curvature, as shown, being substantially spherical about a point X on the axis of rotation of the drum midway between the opposite s ides of the bowl. Within the bowl is located a conveying means in the form of an impeller blade 216 having its outer edge in close proximity to the bowl surface 24 and extending entirely around the drum axis. As shown, this blade is in the form of a flat circular ring, the outer perimeter of which has a radius approximately equal to the radius of thespherical bowl surface 24 fromV point X. The inner edge of the blade is xed to a hub 28 which is rotatably received in a bearing socket 30 o-f an impeller support 32 within and disposed centrally of the bowl, said support being xedly carried by a sleeve 34 extending rearwardly from the drum and housing, within and co-axial with the drum sleeve I4. Bearing 3a is centered on the point X but has its axis Z-Z inclined to the bowl and drum axis Y-Y, at right angles to aplane Q-Q extending through the point X and diagonally through the opposite ends of the bowl at opposite sides of the drum axis. The central plane of the blade 26 coincides with the plane Q-Q and the blade is therefore rotatable in said diagonal plane Q-Q- about the point X in bearing socket 3D.

Relative rotation between the bowl surface 24 and the impeller blade 26 is prevented by means of a raised rib 36 onthe bowl surface, extending from end to end thereof, said rib being received in a slot 33 (Fig, 2) in the outer edge of blade 2B and forming a key along which the blade portion contiguous to slot 3E! is slidable from end to end of the bowl.

The interior of sleeve 34 is provided with a coaxial fixed tube 4U, the rearward end of which projects `from the sleeve and is fixed in a support post 42 on the base i4 of the machine. The slurry to be treated is fed into the projecting end of tube 4B and is discharged from the opposite end of the tube intova chamber l within impeller support 32. Outlet ports 43, 5t through support 32 at opposite sides of bearing socket 3d lead from chamber 46 respectively to discharge nozzles 52, 54 projecting toward the bowl sur# face at opposite sides of blade 26. A liquid overflow pipe 55 pro-jects from rib 36 and extends outwardly through the rib and drum into a gutter formed between two flanges 58 in the housing I2, these flanges having circular inner edges closely tting the outer surface of the drum Il). Blade slot 38 is made sufficiently deeper than rib 35 to clear the inner end of pipe 53.

In operation, the drum is rotated at high speed and the liquid and solids mix to be treated is supplied to the bowl through the nozzles 52, G. By centrifugal force, the mixture is forced outwardly against the bowl forming a so-called poo within the bowl, indicated at P in Figsl 1 and 2, which extends completely around the bowl axis. The depth of the pool is controlled by the height of the overflow pipe 56 from the bowl surface which is somewhat less than the full depth of the bowl at its mid point so that the extreme end edges of the bowl surface are clear of the pool.

Under centrifugal force, a solids fraction S of the mixture in the pool settles against the bowl surface, as indicated in Fig. l. The solids fraction is swept from the pool and the bowl, alternately from the open front end and from the rear end between the spokes of spider I5, by impeller blade 26 which oscillates from end to end of the bowl surface with a sweeping motion, as hereinafter explained. The solids fraction swept from the ends of the bowl isV collected in gutters formed in housing I2 between its end walls and the flanges 58 from which it is withdrawn through suitable outlets (not shown). The remainder of the mixture in the pool, from which the fraction S is thus separated, overflows from thev bowl through pipe 56 into the collecting gutter between flanges 58, from which it is withdrawn through a suitable outlet (not shown).

To facilitate understanding of the operation of impeller blade 26, assume first that the centrifuge drum IB is rotating but impeller support 32 and its sleeve 34 are held stationary. Relative rotation between the blade and the bowl being prevented by engagement of rib 36 and slot 38, the blade is carried by rotation of the bowl about the bearing 30 and its axis Z--Z. Since the plane Q-Q, at right angles to the axis Z-Z, in which the blade edge rotates about the bearing 3i), extends through the opposite end edges of the bowl at opposite sides of the bowl axis, the blade edge oscillates during each 360 of rotation, back and forth across the bowl surface to and between the points of intersection of plane Q-Q with the bowl ends.

The same result is obtained if the drum is held stationary and the sleeve 34 is rotated. The relative position of the parts after 180 of rotation of sleeve 3s relative to the bowl, is partially indicated by dotted lines in Fig. 1.

In any case of relative motion between the bowl and blade on the one hand and bearing 3B on the other, the bearing functions as a rotary cam, inclined to its axis of rotation, to oscillate the blade back and forth across the bowl surface Y with a sweeping motion, diametrically opposite points on the blade edge at all times moving in opposite directions. I

In actual operation, both the drum and the impeller support are normally rotated at slightly different speeds, with the result that the rate of rotation of the blade with respect to the axis Z-Z is reduced to the differential between the two rotational speeds. Thus, if the support is rotated at a lower speed than the drum, the effecty is. the same as if the. support were held stationary and the drum were rotated at the speed dinerential, Conversely, if the support is rotated at a higher speed than the drum, the eiiect is the same as if the drum were held stationary and the support were rotated at the speed differential.

The blade edge, as it oscillates longitudinally of the bowl surface, sweeps settled solids ahead of it, discharging them continuously from both ends of the bowl. As the blade does not rotate with respect to the bowl or the solids bed S, and as the blade travel is short and direct, there is a minimum of rubbing or grinding of the solids by the blade. Moreover, the frictional resistance to the movement of the blade and thereby to the differential rotation of the two rotary bodies is so slight that it is possible to operate sleeves I4 and Si at differential speeds without complex speed reduction gearing, As shown, they are operated by V-belts from a single power shaft (not shown) extending over belt pulley 22 on sleeve id and a belt pulley ill fixed to sleeve 34. Pulley 'ill is shown as of slightly larger diameter than pulley 22 so that if operated from pulleys of equal diameter on the power shaft, sleeve 34 and support 32 will rotate in the same direction as sleeve it and drum Ill but at a slightly lower speed.

Fig. 3 illustrates a modified form of the machine which differs from that of Figs. 1 and 2v principally in the form of the impeller support and in the feeding mechanism. This machine has a centrifugal drum BE! rotatable within a stationaryA housing 32 on a base 84 by means of a driving sleeve 86 connected to the rear end of the drurn bearing SI) projecting rearwardly from the housing. A double V-belt pulley 92 is xed to the rearward end of sleeve 86. Drum is provided with an inner, bowl surface 94 which is conca-.ve longitudinally of the drum axis. As in the embodiment of Fig. 1, the curvature of bowl surface @ii is approximately spherical about pointv X on the axis Y-Y of the drum.

An impeller blade 96 is located within the bowl4 il with its outer Vedge close to the bowl surface. The blade is in the form of a flat ring having its inner rim fast to a cylindrical hub 98 rotatably held on the crank pin portion Ill of a crank shaft |02 by a lock nut IM. Shaft |02 is rotatably received within sleeve 8B and is provided at its rearward end with a driving double V-belt pulley III). Crank pin portion |60 has its axis Z-Z passing through the point X at an incline to the bowl axis Y`-Y. This incline is such that the plane Q-Q of the blade extends diagonally of the bowl, intersecting the opposite end edges of the bowl at oppostie sides of the bowl axis..

Relative rotation between the blade and the bowl is prevented by the ribs I I2 extending across the bowl surface at opposite sides of the bowl axis, each rib being received in a slot |I4 in theadjacent edge of the impeller blade. Each of .the ribs II2 is provided, with an inwardly projecting liquid overflow pipe IIS which opens outwardlyv through the drum into a collecting gutter formed between flanges IIS in housing 82, the inner circular edge of said flanges closely fitting the outer surface of lthe drum. The inner ends of pipes I I6 define the level of .the pool in the bowl.

The front edge of the drum has fast thereto a spider |26, the hub |22 of which forms a chamber |24 into which the mixture to be treated is-fed through a pipe connection |25 nxed through the. front wall of housing 82 and projecting into chamber |24, hub |22 being rotatably journaled onthe pipe I 26. Nozzles |28 extend outwardly from chamber |24 to adjacent the bowl surface, each in the plane of one of the ribs I 2 and of the corresponding blade slot ||4 which is made deep Venough to permit the nozzle to pass through the blade when the aligned portion of the blade is at that end of the bowl.

The operation is the same as described in connection with the machine of Figs. 1 and 2. That is, sleeve 86 and shaft H12 .are rotated in the same direction but at different speeds with the effect that the-drum, bowl and impeller blade are rotated with respect to the impeller support, or vice versa, at the speed differential. Due to the incline of crank shaft pin to bowl axis Y--Y, this relative rotation causes the blade to oscillate with a sweeping motion from end to end of the bowl, directly sweeping the solids fraction from the ends of the bowl through spiders 88 and |20 into collecting gutters in housing 82 at opposite sides of anges IIB. The more uid fraction overflows through pipes ||6 into the gutter between flanges H8.

The changed position of the impeller blade corresponding to a 180 rotation of the support with respect to the bowl and blade from the full line position of Fig. 3 is indicated by dotted lines therein.

As indicated, it is preferred to form the bowl surface with a spherical curvature corresponding to the spherical path described by the blade edge in rotation about the bowl axis. However, this is not essential since, if the bowl surface is formed cylindrical with raised end edges, solids will co1- lect in the bowl between the ends and center beyond the path of the blade, forming a bed with a spherical inner surface which becomes the effective bowl surface swept by the blade. Also, though it is preferred to positively key the blade non-rotatably to the bowl, as by the rib and slot arrangement shown, this may be omitted and the frictional resistance of the solids to rotation of the blade may be relied upon to accomplish, though less reliably, the same function. The differential speed between the bowl and the blade support may, of course, be obtained .through a speed reduction gearing, if desired.

Having now described preferred embodiments of the invention, what I desire to claim and secure by Letters Patent is:

l. A centrifugal separator having in combination a rotary drum forming in its interior an annular centrifugal bowl, an impeller blade mounted within the bowl for rotation therewith about the bowl axis with its edge adjacent the surface of the bowl extending diagonally about the bowl axis substantially from end to end of the bowl, and means acting on said blade, while the blade is rotated about the bowl axis at the rate of rotation of the bowl, tocause said blade to rotate with respect to a second vaxis substantially normal to the plane of said edge at a rate less than the rate of rotation of the bowl, whereby said edge oscillates substantially from end to end of the bowl at said lesser rate to sweep from the bowl endwise thereof a fraction of a material subjected to centrifugal action in the bowl.

2. A centrifugal separator as claimed in claim 1 which includes means interconnecting said bowl and blade against relative rotation while permitting oscillation of the blade edge between the ends of the bowl.

3. A centrifugal separator as claimed in claim 1 wherein the bowl surface has a substantially spherical curvature and said blade edge is substantially circular with a radius approximately equal to the radius of curvature of the bowl surface.

4. A centrifugal separator as claimed in claim 1 which includes means for feeding a material to be treated to the bowl surface at opposite sides of said blade.

5. A centrifugal separator having in combination a rotary drum forming in its interior an annular centrifugal bowl, an impeller within the bowl and rotatable therewith including a blade having a substantially circular outer edge adjacent the bowl surface extending diagonally about the bowl axis substantially from end to end of the bowl, a bearing rotatably mounting said impeller for rotation about an axis substantially normal to the plane of said blade edge so that said edge oscillates substantially from end to end of the bowl in rotating with the bowl to sweep from the bowl endwise thereof a fraction of a material subjected to centrifugal action in the bowl, and means for rotating said bearing about the axis of rotation of the bowl in the direction of rotation of the bowl but at a different speed to reduce the rate of oscillation of said blade edge below the rate of rotation of the bowl.

6. A centrifugal separator as claimed in claim 5 which includes means interconnecting said impeller and said bowl against relative rotation while permitting reciprocation of said blade edge across the bowl surface. V

7. A centrifugal separator as claimed in claim 5 wherein the bowl surfacehas a substantially spherical curvature and said bla-de edge has a radius of curvature substantially equal to the radius of curvature of said surface.

8. A centrifugal separator as claimed in claim 5 which includes means for feeding a material to be treated to the bowl surface at opposite sides of said blade. i

9. A centrifugal separator having in combination a rotary drum forming in its interior an annular centrifugal bowl having its ends raised toward the aXis of rotation thereof, at least one duct opening through the bowl and drum and having its inlet end projecting inwardly from the bowl surface between the raised ends thereof to form the outlet for one fraction of a mixture of liquid and solid received in said bowl and to determine the depth of pool of the mixture maintained in the bowl, and an impeller blade within the bowl and rotatable therewith having an outer edge adjacent the bowl surface curved about the axis of the bowl and movable in a curved path approximately radially equidistant from the midpoint of the bowl axis substantially from end to end of the bowl to remove another fraction of the mixture from the pool and discharge it from an end of the bowl.

10. A centrifugal separator as claimed in claim 9 wherein said bowl surface has a substantially spherical curvature radial to the mid-point of the bowl axis.

11. A centrifugal separator as claimed in claim 9 which includes means for feeding the mixture to be treated to the bowl surface at opposite sides of said blade.

l2. A centrifugal separator as claimed in claim 9 which includes a stationary housing surrounding said drum and provided with compartments at the ends of said drum for receiving said last named fraction and a separate compartment intermediate the ends of the drum for receivin;7 said first named fraction.

EDWARD F. SMAllil'l- 

